Fluke 1623-2, 1625-2 Application Note

Taking care of

an at-risk dam

Application Note

Completed by the U.S. Army Corps of Engineers
(USACE) in 1962 as a flood-control measure, Tuttle
Creek Dam sits on the Big Blue River, five miles
north of Manhattan, Kansas. Made of rolled earth
and rock fill and resting on an alluvial foundation, it’s
about 137 feet high and 7500 feet long. The dam
holds back Tuttle Creek Lake, which amounts to
335,100 acre-ft at normal pool and approximately

1.9 million acre-ft during flood events.

Here’s the problem: It’s 12 miles
from the Humboldt fault zone, a
localized seismic “hot spot” that
has a small but real probabil­ity of producing an earthquake
of magnitude 5.7 to 6.6. Such
an event would cause what’s
known as liquefaction, in which
the earth (mostly silt and sand)
on which the dam rests changes
from a relatively solid base to
what amounts to quicksand.

During the 1989 Loma Prieta
earthquake in San Francisco,
the soil under the city’s Marina
district liquefied, causing many
buildings to collapse. A simi­lar event at Tuttle Creek could
cause the dam to fail. According
to 2006 USACE estimates, this
would release 381,000 cubic
feet of water per second, flood
parts of downtown Manhattan
to depths of 17 feet, result in the
deaths of up to 400 people out
of a population of 13,000, and
cause damages downstream of
$458 million. The dam has even
been featured on The History
Channel’s “Mega-Disasters: Dam
Break” show.

F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y

Bob Frazey uses the Fluke 1630 to check all the grounding wires around the building that all the communications come into from various points around and across
the dam. These include remote sensors, video feeds, and visual and audio warning stations.

In 2002 the Corps set out
to make the dam safe, using a
variety of methods, including
the construction of soil-cement
transverse panels to strengthen
foundation soils beneath the
toe of the dam. But it would
take years to finish that, and in
the meantime the area down­stream would still be at risk.
The answer was to put in place
a Dam Failure Warning System
that would sound an alert in
time for the people to evacuate.

The Corps of Engineers con­tracted for the Tuttle Creek Dam
Failure Warning System with the
global engineering, construc­tion and technical services firm
URS Corporation. With 55,000
employees worldwide, the
company has three divisions:
URS Engineering Corporation;
EG&G, a defense services com­pany; and Washington Division,
a large contracting company
and builder. URS Engineering
Corporation offers services to
rehabilitate and expand public
infrastructure, including sur­face, air, mass transit and rail
transportation networks, and
ports and harbors. The division
also provides program manage­ment; planning, design and
engineering; and construction
and construction-management
services for water supply, con­veyance and treatment systems.

The Dam Failure Warning
System is made up of a number
of components and subsystems,
starting with geotechnical
instruments.

Automated geotechnical
instruments

These devices include sensors to
measure seismic shaking, detect
embankment/foundation defor­mation, and monitor changes in
foundation pore pressures. The
data from these devices is sent
to the Critical Systems Building
(CSB) via radio, and many are
solar-powered, which not only
makes them immune to power
outages but also eliminates
possible voltage surges via ac
power lines.

Pore-pressure sensors

For pressure sensing, URS often
uses vibrating wire piezometers.
Housed in sturdy metal cases
with pointed ends, they are
pushed 30 to 50 feet into the
earth near the toe of the dam.
They are connected via cable
to a solar-powered datalogger
which in turn sends its data
to the central computer in the
CSB for storage and analysis.
The sensors’ output signal is a
frequency, which can be read
at fairly long distances despite
cabling losses. In addition, they
have built-in protection against

lightning surges, and when
coupled with good lightning pro­tection and grounding systems,
give very stable readings for
many years.

But they have a drawback,
says Jim Hummert, Jr., PE, Vice
President-Systems Engineer­ing with URS Corporation: It
takes about one second to get
a reading from each sensor.
While this is not a problem
for applications like long-term
performance monitoring for dam
safety (which generally involves
taking several readings over the
course of a day), it’s too slow for
an early warning system, which
must record a pore pressure
signature immediately following
an earthquake.

“We need to read these
devices more quickly and be
able to process the results
and run through some type of
algorithm or alarm-checking
protocol for notifications,” Hum­mert explains. For that reason
URS added a set of strain gage
pressure sensors with 4-20 mA
output. These can be read 10
to 15 times per second or more
with standard dam-safety data­acquisition equipment.

2 Fluke Corporation Taking care of an at-risk dam

Remote controlled video
cameras

The availability of economi­cal wireless video cameras has
been of great benefit in this
area. In the Dam Failure Warn­ing System, three video cameras
provide remote visual inspection
of the dam spillways, struc­tural elements and weir flows
following an earthquake. They
transmit video via a 5.8 GHz
radio link and receive operator
commands to pan, zoom and
tilt via 900 MHz spread spec­trum radio. Video outputs are
available using IP protocols so
they can be viewed by all the
stakeholders.

Automated data acquisition
system (ADAS)

This solar-powered unit receives
all the geotechnical instru­ment data and transmits alarm
annunciation.

Deformation monitoring
equipment

During an earthquake-induced
failure, the crest of the dam
could drop by as much as 30
feet. The early warning system
includes four ways to monitor
such an event. One is distinctly
low-tech: A string of solar­powered “runway” lights along
the crest and toe of the dam
(officially called “Embankment
Alignment Indicators”), which
can be seen at night.

The second is slightly more
complicated: A linear series of
nested-loop cables is strung
through a series of concrete
weights extending 4000 feet
along the dam crest, buried
about two feet below grade.
Officially called the “Dam Crest
Integrity Monitor,” these are
simple twisted-pair cables
shorted at one end, and their
electrical resistance is con­stantly monitored by the data
acquisition unit. “We measure
the resistance on these cables,
and they’re varying lengths,”
says Hummert, “so if the dam
were to breach we would be
able to tell approximately where
the breech occurred and about
how wide the breach is.”

The third is a set of Time
Domain Reflectometry (TDR)
cables to measure potential
post-earthquake displacement in
the downstream toe area. TDR
cables can be used to measure
variations in soil moisture and
horizontal or vertical deforma­tions continuously along a given
length of cable. Individual cable
lengths are limited to about
2000 ft. This type of device
makes it possible to measure
along a continuum instead of
only at discrete points, which is
a limitation of most geotechni­cal/structural instruments being
used today.

The fourth is a set of auto­mated inclinometers placed
along the toe of the dam. An
inclinometer measures the “tilt”
of a hole or pipe in the hole.
The inclinometer instrument is
slid down this pipe using small
grooves in the pipe. Over time,
if the pipe moves sideways at
some point it indicates that the
ground is moving and shifting
sideways—a clear warning sign
of other issues. Inclinometers are
installed about ten feet apart;
taking repeated readings at each
ten-foot increment shows the

Other features of the system
include:

Dam Safety Status Indicators

•

(DSSIs), which are alert-noti­fication units custom-built for
First Responders.

A web portal which provides

•

remote access to instrument
data, dam safety status, recent
earthquake information, video
camera images, and lake level
data.

The seismically hardened Crit-

•

ical Systems Building, which
integrates the ADAS with
DSSIs and computers at remote
locations. It processes and
transmits alarms, data and
video to the remote users via a
private wide area frame-relay
network and backup satellite
network. All internal com­munication in the CSB is via
Ethernet. The CSB is equipped
with uninterruptible power
supplies and a propane-fueled
backup generator.

A siren warning system with

•

six 4500-Watt solid-state
tone- and voice-capable
sirens located in the evacua­tion zone; siren tones include
voice, tornado warning and

evacuation.
tilt at each level with depth over
time.

Bob Frazey works in one of the sensor service panels that lay across the base of the dam. These service panels are
all low voltage panels that house ground swell sensor communications and support systems. He uses the Fluke 189
DMM to check the 12 V dc battery charging system that comes from a nearby solar panel. He also uses the Fluke
771 Milliamp Process Clamp Meter to check the 4 mA to 20 mA signal from the pressure sensors and transducers.

3 Fluke Corporation Taking care of an at-risk dam

The Fluke 1630 is also used to check the grounding wire on the
mast of the radio antenna and solar charging panel. Frazey also
uses the Fluke 189 DMM with a Fluke i410 current clamp to look
at the current output of the solar panel to the battery charger
inside the service panel.

Indoor tone alert units at

•

facilities that require special
evacuation attention, such as
schools, daycare centers, and
facilities for the elderly and
handicapped.

An education and evacuation

•

plan for nearby communities.

What happens when the
alarm sounds

If the dam’s strong motion
accelerograph (SMA) units detect
ground shaking correspond­ing to a significant earthquake
(greater than about 4.5 mag­nitude), an autodialer will
call key personnel and play a
pre-recorded message detailing
the conditions detected at the
dam. In addition, the DSSI units
will provide remote locations
with information on the status of
the dam using colored indicator
lights to represent various safety
conditions.

If the SMA units detect ground
shaking corresponding to a
severe earthquake (>5.7 magni­tude) and damage to the dam is
detected, the DSSI units will also
display a countdown timer with
a delay of between 30 minutes
and 2 hours before automatic
activation of the downstream
warning sirens. The delay pro­vides time for USACE to assess
the dam and potentially stop
automatic activation (or initiate
manual activation) of the siren
warning system.

Keeping things working
with Fluke equipment

All these subsystems and com­ponents require careful setup,
maintenance and troubleshoot­ing, and the URS people on site
use Fluke equipment almost
exclusively for the purpose. Take
lightning protection and ground­ing, for example. This part of
Kansas is subject to severe
thunderstorms, so surge protec­tion of the equipment is a must.

“We spend a lot of time
designing the grounding
systems and the lightning
protection systems for these
systems,” says Bob Frazey,
field superintendent with URS
Corporation. “These are pretty
sophisticated data acquisition
units, remote-located out on the
embankments of the dam, for
the most part, or down in the
instrumentation galleries or in

the power house,” he continues,
“so when we’re designing the
grounding systems, and the
grounding conductors and so
forth, we’re checking resistance
to ground, bonding resistance
between the various connectors
that we’re using.” Frazey uses a
Fluke model 1630 Earth ground
clamp meter to check equipment
ground and lightning-protection
grounding installation.

Frazey uses a number of
Fluke instruments to check the
4-20 mA measurement loops on
the strain gage soil pore pres­sure sensors and the equipment
they feed. He uses a Fluke 707
Loop Calibrator to check and
calibrate both 4-20 mA instru­ments and controls, and a model
771 process clamp meter to
monitor, test and adjust 4-20 mA
system controls without break­ing into the current. “We always
check and verify that you get
zero and full scale and some
intermediate value as well when
you do the installation,” says
Jerry Zimmer, Senior Consultant
with URS Corp.

Frazey uses a Fluke 189
Digital Multimeter (DMM) with
its accessory Fluke i1010 amp
clamp for general volt ohm test­ing and for checking the output
frequencies of the direct-push
vibrating-wire pressure trans­ducers. He also uses the 189
with an ac/dc amp clamp to
check amperage draw on solar
charging systems and batteries.
There’s another way to check
solar charging systems with the
189, adds Zimmer: Hook every­thing up and then check that
the battery voltage is increasing
over time. “We usually stand
and watch that for five or ten
minutes to make sure things
are moving along like we would
expect,” he explains.

“The 189 DMM is also used
to occasionally check electronic
components and a temperature
probe is used to check small air
conditioning systems on a few
of our pump control boxes,” adds
Frazey.

4 Fluke Corporation Taking care of an at-risk dam

A Fluke Networks MicroScan­ner 2 Cable Verifier and the
Microprobe signal tracer acces­sory are used on Ethernet
systems to make, check and
repair the CAT 5-6 ethernet
cable. The MicroScanner has
been of great help, says Zimmer,
“to verify our Ethernet cables
before those get connected,
because we always make those
to length, we don’t just buy little
3-footers; we’re always string­ing cables out, and I know at
Tuttle Creek, as an example, we
had to verify before we pulled
them through some conduits
underground.” It was the
MicroScanner, he continued, that
alerted them to a problem with
one brand of Ethernet cable con­nectors and led them to change
suppliers. The MicroScanner
is used to test for length to an
open or short, and occasionally
to check and repair coax cable.

Frazey uses a Fluke 971
Temperature Humidity Meter to
monitor environmental condi­tions in dam galleries that
may cause condensation inside
control boxes. In addition, he
has built a mobile electronics
lab and small machine shop to
use when installing and doing
maintenance on the systems.

Results

The Tuttle Creek Dam Failure
Warning System was completed
in March 2005. The system won
the 2006 grand award with the
American Consulting Engineers
Council (Missouri chapter of
ACEC). URS has put together a
number of similar systems in
other locations, including the
Wolf Creek dam in Kentucky.

The foundation modifica­tion work at the dam site has
recently been completed. Later

this year, once the walls have
hardened and the buried collec­tor system has been completed,
the DFWS will be decom­missioned. The siren system
is being turned over to Riley
County and will become part of
the existing county tornado siren
warning system. In the mean
time, URS continues to provide
operations and maintenance
support.

The URS people seem pretty
well sold on Fluke equipment.
“I’ve recommended Fluke equip­ment for a number of years,”
says Zimmer, “but when we’re
outside working on equipment I
don’t even think about the thing
not working, because I know
that Fluke stuff just works all
the time. So I always feel really
good, I always buy that, because
I don’t have to worry about it
breaking.”

5 Fluke Corporation Taking care of an at-risk dam

Fluke. Keeping your world
up and running.

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Printed in U.S.A. 1/2010 3610922A A-EN-N

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